The present invention relates to a method and apparatus for the fine or micro-finish machining of cylindrical or conical surfaces on workpieces, especially on the inner and outer races of roller bearings or tapered thrust bearings. The invention involves rotating the workpiece and providing a honing tool which acts on the surface of the workpiece by executing a swinging or oscillating motion (first swinging motion) in a plane parallel to the surface of the workpiece.
This type of micro-finish machining (super finishing, honing) performed on the races of cylindrical roller bearings or tapered thrust bearings improves the surface previously obtained by, for example, grinding, and also compensates for errors in roundness, especially short range errors.
The known state-of-the-art possesses certain disadvantages which shall now be explained with the aid of FIG. 1. In FIG. 1 there is shown the inner race 3 of a cylindrical roller bearing, whose track or raceway 2 is to be treated. The oscillating motion of the honing tool acting on this raceway 2 is limited by the two shoulders 2' and 2". These two shoulders 2' and 2" do not permit exceeding the width of the side ends of the raceway. The width of the honing tool used is approximately equal to the width D of the raceway 2 minus the amplitude of the oscillation of the honing tool without considering a small clearance for safety's sake. After the treatment described above, the raceway, which began as a flat surface 2, i.e., a straight ground generatrix line, has usually a somewhat concave appearance as shown in FIG. 1 by the dashed line A, i.e., a concave appearance to the generatrix line. This is due to the fact that during its oscillation, the honing tool acts on the middle region of the raceway 2 somewhat longer than on the outer regions. However, surfaces generated by a generatrix line of this type are not desirable as they cause very high pressures of the roller bearing rolling element at those places of the raceway which are critical anyway.
There is therefore a need for a method and an apparatus which make possible the machining of such surfaces without causing the formation of the slightly concave generatrix line as shown by the dashed line A. in FIG. 1. It might even be desirable to let the generatrix line have the appearance of a slightly convex form as is shown by the dashed line C in FIG. 1 so that during full loading of the bearing, the raceway 2 will be subjected to approximately uniform surface pressure over the entire width of the raceway. A surface generated by this type of generatrix line tends to diminish load peaks which would occur at the two sides of the raceway if the raceway were entirely straight. Therefore, it would be desirable to have a method and apparatus according to which the raceway is machined so that when viewed in transverse cross section the bottom surface of the raceway is preferably slightly convex as shown by the dashed line C.